A spectacular regular season that ended with their first Presidents' Trophy in 24 years is perilously close to going up in the smoke of trivia for next season's Boston Bruins yearbook.

They have lost two of three to the Montreal Canadiens with Game 4 Thursday night at the Bell Centre (NBCSN, 7:30 p.m.).

Is it a must-win?

No. We've seen the Bruins climb out of their coffin before, so it would be silly to suggest ahead of mathematical certainty, but with the enthused Canadiens reaching for the penultimate nail, there is no time like the present for the Bruins' best.

But what if their best is not enough? These are not your 2013 Bruins, much less your Stanley Cup team from 2011. They are too young in the wrong places, and the Canadiens are doing a fabulous job at exploiting their inexperience.

This vulnerability — and the resultant unrest in Bruins Nation with all aspects of their game — stems from Dennis Seidenberg's knee injury. The defenseman's Dec. 27, garbage-time collision with Ottawa Senators forward Cory Conacher is the big bang of all that ails the Bruins in this second-round series.

So there's no point picking on the power play, which after going a league-leading 33 percent against the Red Wings in the first round of the playoffs is now 0-for-6 against Montreal.

Social media has Zdeno Chara aging and David Krejci slumping. Suddenly whatever tends to ail this team is no longer forgiveable.

Was it really that different with these players last year?

A slow start is nothing new for the Krejci line. The center scored in last year's series against Toronto but not against New York, then scored against Pittsburgh but not against Chicago.

Inconsistency at any and all positions is magnified because Seidenberg isn't back there and neither is Andrew Ference to make ordinary nights forgettable with the absurd stability their play provided.

Now the Bruins are finding out how the other half lives, with a blue line anchored by Chara and Johnny Boychuk and augmented by four guys with less than two full NHL seasons under their belts and a second-tier rental.

When Kevan Miller got crossed up with Tuukka Rask behind the net in the first period of Game 3, a possession battle ensued in the corner and — who else — P.K. Subban came up with it and made a great play to Tomas Plekanec for the first goal.

Then Dougie Hamilton didn't know that Subban was about to exit the penalty box and Subban converted his breakaway.

Preferring journeyman Andrej Meszaros to Matt Bartkowski has brought qualified rewards. Meszaros made a nifty cutoff early in Game 3 on Max Pacioretty, but when Mike Weaver blocked his shot from the left point the Canadiens were back off to the races. Late in the game, Meszaros shot the puck and Jarome Iginla tipped it past Carey Price to put the outcome in doubt, albeit briefly.

Page 2 of 2 - If Meszaros is not the answer on the second pairing, more youth certainly isn't.

Don't let the logo fool you. Sometimes the names on the backs of the jerseys are as important as the name on the front.

Without Seidenberg, core players' off nights have been magnified.

The Stanley Cup is an abused, banged-up and imperfect trophy, so much so that the rim of the bowl sitting atop it is physically warped. But one blemish you cannot find anywhere on the Cup is a defense as young and mistake-prone as the one the Bruins are trying to win with right now.

The Bruins are not only on the ropes against the Canadiens, they're on the ropes against history.